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January 2010 Supplement
Surveillance of Aortic Stent Grafts
With the proper patient follow-up regimen, new imaging modalities are optimizing the current standard of care for EVAR surveillance.
With increasing application of aortic stent graft placement (EVAR) for aortic aneurysm repair comes the potential for more long-term complications. In light of health care expenditure debates, an economical yet safe protocol to monitor the patient and device after EVAR is critical. Consensus guidelines by Chaikof et al1 recommend obtaining a computed tomographic angiogram (CTA) every 5 years for open surgical repair (OSR) of an abdominal aortic aneurysm (AAA), while EVAR requires yearly surveillance for endoleaks and device migration. During the first postoperative year, CTA—the current gold standard—at 1 month and 1 year is recommended unless an endoleak is detected. If a type II endoleak is detected, CTA at 6-month intervals is recommended. After 1 to 3 years without endoleak or aneurysm sac expansion, yearly duplex ultrasound can be considered if surveillance can be performed and interpreted by experienced staff.1,2
WHY DOES SURVEILLANCE MATTER?
Recent analysis from our institution of 270 ruptures
after EVAR revealed that most ruptures will occur in the
first 2 to 3 years after implantation. Endoleaks in which
the aneurysm sac continues to fill despite EVAR were the
most common cause of rupture. Only six of these
endoleaks were type II endoleaks. The majority of
endoleaks leading to rupture were type I and III from
leaks at proximal and distal seal zones or component separation,
respectively.3 Type I and type III endoleaks require
timely intervention. However, many of these dangerous
endoleaks were not detected due to inadequate followup.
Endovascular or open treatment of type II endoleaks
should be considered after persistence for > 6 months.1
Device migration was the second most common cause of
rupture. The fact that failure of follow-up contributed to
rupture in 43 patients underscores the necessity of a surveillance
protocol.3
WHAT IS THE IDEAL MODALITY FOR EVAR
SURVEILLANCE?
The ideal EVAR follow-up modality remains controversial.
Proponents of yearly surveillance with CTA emphasize
the superior reproducibility, convenience, and a clearer
picture of graft integrity and morphology of the
aneurysm. CTA sensitivity is 92% with specificity 90%.4
Ultrasound follow-up regimens cite decreased cost,
decreased radiation exposure, and similar rates of
endoleak detection as benefits of ultrasound over CTA.2,5
The sensitivity of color duplex for endoleaks has been
reported to be 52% to 81% with a specificity of 89% to
97%, with a positive predictive value of 88% and a negative
predictive value of 100%.6,7 With yearly CTA within
the first 5 years, 9.3% of patients will benefit from the
detection and intervention upon endoleaks.8 Chaer et al
support that surveillance solely by ultrasound is effective
in detecting endoleaks especially after the first 3 years.2
WHAT DOES THE FUTURE OF EVAR
SURVEILLANCE LOOK LIKE?
Follow-up CTA at 1 month and 1 year after EVAR is
likely a legacy of the US pivotal trials conducted for FDA
device approval. Most clinicians have used the 1-month,
6-month, and yearly CTA follow-up surveillance regimen
mandated in the trials in their routine clinical practice.
There are very little data supporting this regimen, and
many centers, including our own, now routinely eliminate
the 1-month CTA if the procedural angiogram was
pristine. Our current practice is to use both ultrasound
and CTA after 3 to 6 months and then yearly for the next
3 years. Adjustments are considered in cases of expansion
or large type II endoleaks. After 36 months without
aneurysm expansion or endoleak, annual ultrasound is a
safe mode of surveillance. Any suspicion for aneurysm
expansion or graft abnormality should prompt CTA.
Failure of the follow-up regimen clearly results in preventable
aneurysm rupture (Figure 1). The best regimen
is one that is frequent enough to detect endoleaks within
the first 3 to 5 years and is individualized to the patient's
habitus and reliability.
Newer imaging modalities are showing promise. Contrast-enhanced ultrasound should increase the sensitivity and specificity and enable ultrasound to continue to replace CTA as the preferred method. At Yale, all of our follow-up imaging is performed with extensive threedimensional postprocessing and examined by both a radiologist and vascular surgeon. This collaborative approach has clearly improved our readings and allowed subtle findings to be more widely recognized and acted upon.
Ensuring that this follow-up happens is more important and less expensive than any imaging modality—yet it is underappreciated. Obviously, a patient lost to followup will never have an asymptomatic endoleak detected before rupture. As our group has previously published, the majority of patients who experience rupture did so after missing one or more follow-up intervals. Industry has begun to recognize this fact. Medtronic Vascular (Santa Rosa, CA) has introduced StentGraftTracker and 3D Recon (in partnership with Vital Images, Minnetonka, MN) in an effort to ensure patients treated with their devices achieve optimal surveillance (Figure 2). Whether one chooses to use a service from industry or simply create one's own system to ensure proper follow-up, surveillance cannot be overemphasized.
Carter Freiburg, MD, is a vascular surgery fellow in the Section of Vascular Surgery at Yale University School of Medicine in New Haven, Connecticut.
Bart E. Muhs, MD, PhD, is Assistant Professor of Vascular Surgery and Radiology and Co-Director of Endovascular Surgery, Department of Surgery, Section of Vascular Surgery at Yale University School of Medicine in New Haven, Connecticut. Dr. Muhs may be reached at (203) 785-2564; bart.muhs@yale.edu.
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